This invention relates to a process for increasing the average reaction rate of reduction of UO.sub.2 F.sub.2.
UO.sub.2 F.sub.2 is an important material used in the nuclear fuel cycle for nuclear power reactors. An important chemical reaction of UO.sub.2 F.sub.2 is reduction to UO.sub.2 for use as nuclear fuel. This reduction is also important in the Fluorox process which is a scheme to generate UF.sub.6 for subsequent isotope enrichment without the use of elemental fluorine.
The reactions of the Fluorox process form the basis of a commercial process for the production of UF.sub.6 by a method not requiring the use of fluorine, see e.g. L. M. Ferris, J. Amer. Chem. Soc. 79, 5419 (1975). The reactions which comprise the process are: EQU 2UF.sub.4 + O.sub.2 .fwdarw. UO.sub.2 F.sub.2 + UF.sub.6 ( 1) EQU uo.sub.2 f.sub.2 + h.sub.2 .fwdarw. uo.sub.2 + 2hf (2) EQU uo.sub.2 + 4hf .fwdarw. uf.sub.4 + 2h.sub.2 o (3)
all of these reactions must be carried out at high temperatures in order that reasonable quantities of the desired product are produced.
The utility of the Fluorox process in general is in part limited by rates of this reduction reaction. An increased rate of reaction of UO.sub.2 F.sub.2 toward reduction would be therefore desirable.
In an attempt to increase the rate of reactions 1 and 2, solid heterogeneous catalysts have been added, see e.g. A. Ekstrom, G. E. Batley and D. A. Johnson, J. of Catalysis 34, 106 (1974); ibid. 34, 368 (1974). While this has been successful, the presence of this second solid phase would require elaborate separation procedures to free the desired product from the catalyst material in a commercial application.
Our invention includes a method to increase the rate of reaction 2 by means of a treatment of the UO.sub.2 F.sub.2 employed.
During the thermal decomposition of a group of complexes which are defined in more detail below, an increase in the surface area of the UO.sub.2 F.sub.2 was noted. This increased surface area of the UO.sub.2 F.sub.2 implied that the recovered UO.sub.2 F.sub.2 should be more reactive to subsequent chemical reactions of the solid-gas and solid-liquid types, with the solid being UO.sub.2 F.sub.2.
However, this is only partially true. The prior art includes a French patent, French 2,045,692, filed June 20, 1969, issued Mar. 5, 1971, in which water vapor treatment of uranyl fluoride powder at 60.degree. C in H.sub.2 O vapor increase surface area of UO.sub.2 F.sub.2 from .about.0.3 m.sup.2 /g to 23. m.sup.2 /g. It can be seen from our Table I that the average reaction rate of reduction decreases rather than increases when a treatment with water vapor is employed.
The present invention discloses a process for increasing the rate of reduction.